The present invention relates to a method of monitoring tire pressure monitoring systems in a motor vehicle having both a direct pressure measuring system and an indirect pressure measuring system, as well as to a computer program product containing the method therein.
Tire pressure monitoring systems are used at an increasing rate in up-to-date vehicles in order to improve safety. On the one hand, so-called direct tire pressure monitoring systems are known in the art which monitor the tire inflation pressure by means of pressure modules in the vehicle tires. Further, so-called indirect tire pressure monitoring systems are known in the art, e.g. from WO 01/87647 A1, U.S. Pat. No. 6,385,553 B1, and EP 0 832 767 B1, which determine the tire inflation pressure from rotational speed data (wheel speed, angular velocity, frequency, etc.) of the vehicle wheels. DE 100 60 392 A1 also discloses a tire pressure monitoring system which describes a combination of an indirect tire pressure monitoring system and a reduced direct tire pressure monitoring system. This tire pressure monitoring system uses, on the one hand, the wheel speed data of wheel sensors which are already provided in a vehicle with an anti-lock system (ABS), while, on the other hand, it uses directly measured tire inflation pressures which are provided in one to two pressure modules in the vehicle tires in order to detect tire inflation pressure loss. Thus, the tire pressure monitoring system described in DE 100 60 392 A1 includes two tire pressure monitoring systems (direct and indirect) which are designed independently of one another, and each of these tire pressure monitoring systems generates a warning signal independently of the other tire pressure monitoring system, while taking into consideration defined evaluation criteria.
The advantage of the tire pressure monitoring system with direct measurement (TPMS) involves that tire inflation pressure loss is detected on each individual wheel and on a combination of optional wheels. However, this system suffers from the shortcoming that the required pressure modules in the tires in general are not designed redundantly or, respectively, that the pressure modules are not monitored, with the possible result of omission of alarms or the occurrence of spurious alarms as far as tire inflation pressure loss is concerned.
As has been described hereinabove, the tire pressure monitoring system with indirect measurement is based on the rotational speed data of the rotational speed sensors which are provided in an anti-lock system (ABS). These wheel speed sensors are monitored in a per se known fashion in the anti-lock system (ABS). This condition allows detecting a possible defect of one or more of the wheel speed sensors, with the result that spurious alarms due to defective wheel speed sensors are almost ruled out. It is, however, disadvantageous in this system that a simultaneous tire inflation pressure loss on all wheels cannot be detected under certain circumstances. The system detects tire inflation pressure loss by way of different wheel speeds of the individual wheels, and a wheel suffering from tire inflation pressure loss rotates faster than a wheel without tire inflation pressure loss. If all wheels exhibit the same tire inflation pressure loss, the system does not detect this simultaneous tire inflation pressure loss because the difference in rotational speeds is missing.